Semiconductor nanocrystals constitute a novel class of materials with physical properties that are significantly different from those of bulk materials. The electronic structure of semiconductor nanocrystals is strongly dependent on the nanocrystal size and shape providing additional options to design and optimize material properties [Murray et al., Ann. Rev. Mater. Sci., 30, 542 (2000)]. Moreover, the ability of semiconductor nanocrystals to form stable colloidal solutions allows their integration into electronic devices by relatively inexpensive and high-throughput solution based processes like spin-coating, dip-coating, drop-casting and jet-printing. The films of close-packed nanocrystals exhibit extremely poor conductivities [Morgan et al., Phys. Rev. B. 66, 075339 (2002)] hindering their application in electronic devices. Recently it has been shown that electrochemical doping of semiconductor nanocrystals results in significant improvement of their conductivity [Yu et al., Science 300, 1277 (2003), Yu et al., Phys. Rev. Lett. 92, 216802 (2004)]. However, electrochemical doping requires the presence of liquid electrolyte, and may not be suitable for use in solid state electronic devices.
Semiconductor nanowires [Lieber et al., US Published Application US 2002/0130311 A1] together with carbon nanotubes are considered as important elements of nanoelectronics. The previous studies involved in situ n-doping of semiconductor nanowires during their growth from gas-phase precursors [Greytak et al., Appl. Phys. Lett. 84, 4176 (2004)]. However, it is not easy or possible to vary in a controllable manner the doping level along the nanowire using gas phase doping after the nanowire has been integrated into a device because the higher temperatures typically used in gas phase doping may not be compatible with device processing. Alternative approaches such as solution phase processing provide various advantages, one of which is the ability to readily control the doping level along the nanowire at temperatures compatible with device processing.